I have a setup of HAP AC(client) to HAP AC3(AP) which worked very well for a very long time.
I replaced the HAP AC(Client) into HAP AX3 to achieve better performance (I could not get an AC3).

Since I replaced the HAP AC to HAP AX3 I got a weird behavior of the wifi link drops every day couple times.
(this link is between the Servers rack to the WAN connection)

I tried to upgrade the HAP AC3 and the AX3 to v7.13 for the sake of testing and used the new wifi ac package on the HAP AC3.
It didn't last too long and the wifi connection started dropping again.
One morning my kids woke me up since I got about 2 dozen messages that the connection to the server was down.

the message on the client side is "disconnected reason code 3, -65 ..".
I am not sure what is the root cause for this issue and I think it's one of couple:
* configuration problem
* wifi interferences
* Software bug

Please try to help me debug this issue.

Thanks,

OK, So first of all for all the assistance in the Discord wifi channel.
I respect each and everyone who made a response to help me first asses the options.
The main difficulty was that it was a RouterOS to RouterOS single device connection and non an Iphone or laptop or android or any other client which can have some unexpected behavior that is out or Mikrotik jurisdiction.

To understand the tests I made and each one of the results I will attach the wifi config and channel and security profiles below in code tag.

The issue I was having was continues disconnections between HAP AX3 to HAP AX3 with static IP addresses on each end
When I used the profile:
* default_5ghz_skip_dfs

The channel that was selected by RouterOS was: 5805/ax/eeeC ie with lowe txpowe ie 8.


Which the in-stability was observed.
It took a while to read in couple places couple "advices" how to resolve the "issue" ie "code 3" which doesn't help by itself to resolved the problem.
Advices were "use auto channel" or "use 24h group key update" and couple other ideas.
These were useful directions however these were not relevant to my issue.
After trying couple things I did a reset to the wifi settings and started from 0.
I was suspecting tx power but was sure that the device choose the right tx power and overlooked it to be only 8 DB ie about 50mw.
After scanning the channels in the room(it's one side to the other with less then 10 Meter between the devices..) and the result of avg -95 ie:


I got the suggestion to take these with a grain of salt since it's a 5Ghz band on a AX3 device which has big antennas and the 5Ghz sensitivity is kid of this way.
For me it made sense since the mobile phone on the other AP ( HAP AC3 ) worked fine for more than year and a half now.
(The issues started between the HAP AX3 to the HAP AC3)

After trying to set the channel manually to 5500 the skip DFS channels settings told me there are no available channels and I started understanding that I don't understand something about the new AX wifi channels and bands.
I took the time to read an article from a suggestion in the Discord channel ie:
https://www.wiisfi.com/

And things started to make more sense after reading it.

After all of this I came with the next profiles for testing and once I have used the current configuration it took about a minute to start the 5ghz wifi (DFS check) but then the 5500 channel was on with 24 DB which is a little bit more then 100mw which would be OK for this distance but would work for half the distance compared to 2.4 Ghz with the same Db.
But, the quality is what matter... not the volume..

Anyway for the past 48 Hours since I have changed the configuration the connection is stable and it's probably due to low TX power and wrongly skipping the DFS channel tests.


Thanks to:
@drmessano6
@Maigonis - LV
@Samot

And all the others in the discord #wifi channel for their patience and suggestions which helped me to find out what was the root cause for my specific issue.

In one area we are all experts and in the other areas other are better then us and can help guide us finding the right path to success.